Crystal structure of uranyl μ3-oxoacetate [(UO2)3(μ3-O)2(OOCCH3)2(H2O)2]

The crystal structure of [(UO₂)₃(₃-O)₂(OOCCH₃)₂(H₂O)₂] consists of uranium coordination polyhedra (CPs) combined via common equatorial edges into ribbons, with ₃-O atoms being common for three CPs. The structure was compared with that of known complexes with ₃-oxo atoms.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 396–400.Original Russian Text Copyright © 2004 by Charushnikova, Krot, Starikova.     

Formation of Al3Ti/Mg composite by powder metallurgy of Mg–Al–Ti system

Abstract

An in situ titanium trialuminide (Al₃Ti)-particle-reinforced magnesium matrix composite has been successfully fabricated by the powder metallurgy of a Mg–Al–Ti system. The reaction processes and formation mechanism for synthesizing the composite were studied by differential scanning calorimetry (DSC), x-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Al₃Ti particles are found to be synthesized in situ in the Mg alloy matrix. During the reaction sintering of the Mg–Al–Ti system, Al₃Ti particles are formed through the reaction of liquid Al with as-dissolved Ti around the Ti particles. The formed intermetallic particles accumulate at the original sites of the Ti particles. As sintering time increases, the accumulated intermetallic particles disperse and reach a relatively homogeneous distribution in the matrix. It is found that the reaction process of the Mg–Al–Ti system is almost the same as that of the Al–Ti system. Mg also acts as a catalytic agent and a diluent in the reactions and shifts the reactions of Al and Ti to lower temperatures. An additional amount of Al is required for eliminating residual Ti and solid-solution strengthening of the Mg matrix.     

稀土永磁材料Sm3(Fe,Ti,Co)29Nx

研究了Sm3(Fe,Ti,Co)29母合金的制备工艺,并对合金元素的选择及添加量进行了探讨.试验研究发现Ti元素可有效抑制α-Fe的生成并起到稳定Sm-Fe 329相的作用;熔炼时至少熔炼四遍可得到组织均匀的铸态试样;合理设计加料顺序可以减小Sm的挥发量,多加入20%～30%的Sm可有效的补偿Sm的挥发.成功的制备了Sm3(Fe,Ti,Co)29 329相母合金.     

Magnetic, electrical, and optical properties of (HgS)1.5(Al2S3)0.5?Mn? and (HgS)1.5(In2S3)0.5?Mn? crystals

We have studied the magnetic, electrical, and optical properties of (HgS)_1.5(Al₂S₃)_0.5〈Mn〉 and (HgS)_1.5(In₂S₃)_0.5〈Mn〉 crystals and determined their magnetic and band structure parameters. The magnetic (Faraday method) and transport (four-probe method) properties of the (HgS)_1.5(Al₂S₃)_0.5〈Mn〉 and (HgS)_1.5(In₂S₃)_0.5〈Mn〉 crystals were investigated in the ranges T = 77−300 K and H = 20−320 kA/m. The magnetic susceptibility data suggest that the magnetic properties of the crystals can be understood in terms of Mn-S-Mn-S clusters. The Hall coefficient of the crystals is temperature-independent. The electrical conductivity of (HgS)_1.5(Al₂S₃)_0.5〈Mn〉 varies little with temperature and has a maximum, and that of (HgS)_1.5(In₂S₃)0.5〈Mn〉 shows metallic behavior and is a nearly linear function of temperature. The thermopower of the crystals increases with temperature. Optical data attest to direct allowed interband optical transitions. The magnetic and band structure parameters of the crystals are determined.     

Microwave-assisted preparation of Ca6Si6O17(OH)2 and β-CaSiO3 nanobelts

Xonotlite (Ca₆Si₆O₁₇(OH)₂) nanobelts were synthesized by a microwave-assisted hydrothermal method at 180 °C for 90 min independent of the feeding molar ratio of Ca(NO₃)₂·4H₂O to Na₂SiO₃·9H₂O in the range of 0.8-3.0. Crystalline wollastonite (β-CaSiO₃) nanobelts were obtained by microwave thermal transformation of Ca₆Si₆O₁₇(OH)₂ nanobelts at 800 °C for 2 h. Ca₆Si₆O₁₇(OH)₂ nanobelts were used as both the precursor and the template for the preparation of β-CaSiO₃ nanobelts. The morphology and size of Ca₆Si₆O₁₇(OH)₂ nanobelts could be well preserved during the microwave thermal transformation process. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED).     

Synthesis of (Zn,Mg)TiO3–TiO2 composite ceramics for multilayer ceramic capacitors

(Zn_0.8Mg_0.2)TiO₃–xTiO₂ composite ceramics has been prepared via the solid-phase synthesis method. TiO₂ was employed to tone temperature coefficient of resonant frequency (τ_f) and stabilize hexagonal (Zn, Mg)TiO₃ phase. 3ZnO–B₂O₃ was effective to promote sintering. The movement of grain boundary was obvious because of the liquid phase sintering. The scanning electron microscope (SEM) photographs and energy dispersive spectrometer (EDS) patterns showed that segregation and precipitation of dissociative (Zn, Mg)TiO₃ grains occurred at grain boundary during sintering. SnO₂ was used as inhibitor to prevent the grain boundary from moving. The dielectric behaviors of specimen strongly depended on structural transition and microstructure. We found that 1.0 wt.% 3ZnO–B₂O₃ doped (Zn, Mg)TiO₃–0.25TiO₂ ceramics with 0.1 wt.% SnO₂ additive displayed excellent dielectric properties (at 1000 °C): ?_r = 27.7, Q × f = 65,490 GHz (at 6.07 GHz) and τ_f = −8.88 ppm °C⁻¹. The above-mentioned material was applied successfully to make multilayer ceramic capacitors (MLCCs), which exhibited an excellent electrical property. The self-resonance frequency (SRF) and equivalent series resistance (ESR) of capacitor decreased with capacitance increasing, and the quality factor (Q) of capacitor reduced as frequency or capacity increased.     

Crystal structure of a double Np(V) and Co(NH3)63+ maleate, Co(NH3)6[NpO2(HL)2(H2O)3](HL)2?H2O [L = OOC(HC)2COO]

Crystal structure of a double Np(V) and Co(NH₃) ₆ ³⁺ maleate Co(NH₃)₆[NpO₂(HL)₂(H₂O)₃](HL)₂H₂O [L = OOC(HC)₂COO] was studied. The crystal structure consists of complex anions [NpO₂(HL)₂(H₂O)₃]^–, HL^– anions, [Co(NH₃)₆]³⁺ cations, and water molecules of crystallization. Hydrogen bonds in which proton donors are water molecules and hexaamminecobalt cations link structural fragments to form a 3D network. The coordination polyhedra of the Np(V) atoms are pentagonal bipyramids whose equatorial planes are formed by oxygen atoms of two HL^– anions and three water molecules. Four crystallographically independent maleate anions were identified in the structure. Two of these anions enter into the Np(V) surrounding, and their coordination capacity is 1.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 521–523.Original Russian Text Copyright © 2004 by Charushnikova, Krot, Starikova.     

Properties of electrodeposited Ni–B–Al2O3 composite coatings

Ni–B coatings have gained a great deal of attraction due to their promising mechanical properties. Owing to tempting properties, Ni–B coatings have succeeded to find their applications in automotive, aerospace, petrochemical, plastic, optics, nuclear, electronics, computer, textile, paper, food and printing industries. Despite having promising properties, further improvement in their properties is essential so that more challenging requirements and new developments can be successfully addressed. In the present study, novel Ni–B–Al₂O₃ composite coatings have been synthesized through electrodeposition process by reinforcing Ni–B matrix with Al₂O₃ particles. A comparison of properties of Ni–B and Ni–B–Al₂O₃ coatings in their as deposited states is presented to elucidate the beneficial role of Al₂O₃ addition. The structural analyses indicate that Ni–B coatings exhibit a single broad peak indicative of an amorphous structure. However, the addition of Al₂O₃ into Ni–B matrix considerably improves the crystallinity of the deposit. The surface morphology study reveals the formation of uniform, dense and fine-grained deposit in both Ni–B and Ni–B–Al₂O₃ composite coatings. However, addition of Al₂O₃ particles into Ni–B coatings results in high surface roughness. The nanoindentation results demonstrates that the addition of Al₂O₃ into Ni–B matrix results in significant improvement in mechanical properties (hardness and modulus of elasticity) which may be attributed to dispersion hardening of Ni–B matrix by hard Al₂O₃ particles. The linear polarization tests confirm that the addition of Al₂O₃ improves the corrosion resistance of Ni–B coatings. This improvement in corrosion behavior may be attributed to the reduction in active area of Ni–B matrix by the presence of inactive Al₂O₃ particles.     

Properties of (Bi2Sb5Se3Te6I3)1 ? xMx (M = Ce, Pr) solid solutions

The effect of doping with Ce and Pr on the physicochemical properties of Bi₂Sb₅Se₃Te₆I₃ has been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements. The results demonstrate that n-type Bi₂Sb₅Se₃Te₆I₃ dissolves 3.5 at % Ce. The Bi₂Sb₅Se₃Te₆I₃-Ce system has a eutectic at 10 mol % Ce, which melts at 360°C. The Pr solubility in Bi₂Sb₅Se₃Te₆I₃ is 4 at %. This system has a peritectic point at 10 at % Pr, with a peritectic temperature of 550°C.     

Structure and electrical properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Bi0.5(Na0.82K0.18)0.5TiO3–BiAlO3 lead free piezoelectric ceramics

0.09(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–(0.01 − x) Bi_0.5(Na_0.82K_0.18)_0.5TiO₃–x BiAlO₃ (BNBKT–xBA) lead-free piezoelectric ceramics were synthesized by conventional solid-state reaction processes. Structure, ferroelectric and piezoelectric properties of BNBKT–xBA ceramics were investigated. X-ray diffraction data shows that BNBKT–xBA ceramics form the pure perovskite phases and the ceramics have the morphotropic phase boundary when x ≤ 0.030. At room temperature, the BNBKT–xBA ceramics at x = 0.030 have better electrical properties, the piezoelectric constant d₃₃ and planar coupling factor k_p of BNBKT–xBA ceramics reaches peak values at x = 0.030: d₃₃ = 217 pC N⁻¹, k_p = 0.308. The remnant polarization P_r, mechanical quality factor Q_m and relative dielectric constant ?_r of BNBKT–xBA ceramics at x = 0.030 attains 33.8 μC cm⁻², 133 and 928 (100 KHz), respectively. As BA content increase, the depolarization temperature T_d shift toward lower temperature, and T_d of BNBKT–xBA ceramics with x = 0.030 decreased to 55 °C.     

Synthesis,structure and optical studies of inorganic–organic hybrid semiconductor,NH3(CH2)12NH3PbI4

Synthesis, crystal structure and optical properties of two-dimensional layered inorganic–organic hybrid NH₃(CH₂)₁₂NH₃PbI₄ are presented. Intercalation strategy has also been used to fabricate single crystal and thin films of the same. As thin film, they are well oriented and stacked along the [l 0 0] direction with strong room-temperature excitonic absorption and emission characteristics. Exciton features were correlated with the relative inorganic network crumpling and conformation of alkylammonium chains. The structural features are compared with those of similar hybrid, (H(CH₂)₁₂NH₃)₂PbI₄.     

FeVO4/Cu3(BTC)2(H2O)3异质结制备及光催化性能

以Cu片和1, 3, 5-苯三甲酸为原料,电化学法制备经典Cu-MOF材料Cu₃(BTC)₂(H₂O)₃,即HKUST-1,作为基底金属有机框架材料(MOFs),采用室温沉积法制备FeVO₄/HKUST-1异质结复合材料,通过XRD、SEM、BET、UV-Vis DRS等对其晶体结构、形貌、比表面积、光吸收性能等进行了表征。结果表明:FeVO₄与HKUST-1复合形成异质结后,有利于光生电子-空穴的产生和转移,对目标染料污染物罗丹明B(RhB)的降解性能显著增强。可见光照射120 min后,异质结体系中RhB的降解率可达93%,而单一FeVO₄或HKUST-1体系中仅为12%和5%。此外,对材料的组成比例进行了优化,当FeVO₄与HKUST-1摩尔比为1∶1时,制备的FeVO₄/HKUST-1复合材料具有最佳的光催化性能。进一步,考察了其循环使用的稳定性,循环5次后对RhB的降解效率仍保持在90%以上,稳定性良好。      

Self-propagating high-temperature synthesis of Y2O3 powders from Y(NO3)3x(CH3COO)3(1 ? x) · nH2O

We have studied the self-propagating high-temperature synthesis (SHS) of yttrium oxide from Y(NO₃)_3x (CH₃COO)_{3(1 − x)} · nH₂O (0.3 ≤ x ≤ 0.7) acetate nitrates, calculated their standard enthalpies of formation using the method of valence states of atoms in a chemical compound, and compared calculated and experimentally determined yttrium oxide SHS temperatures. Using thermogravimetry and differential scanning calorimetry data and thermodynamic analysis, we have determined the optimal range of yttrium acetate nitrate compositions for the SHS of Y₂O₃ powder.     

EPDM/Al(OH)3 复合材料界面结构参数表征研究

采用动态力学分析(DMA ) 研究了EPDM/Al(OH)₃ 复合材料的界面结构参数, 提出了用DMA 分析估算复合材料界面层厚度的新方法, 讨论了Al(OH)₃ 粒子表面状态对EPDM/Al(OH)₃ 复合材料界面结构参数的影响。     

Effect of Nb?+?Ti coating on the wetting behavior, interfacial microstructure, and mechanical properties of Al/Al2O3 joints

The subject of the work was to study the effect of Nb + Ti thin film deposited by PVD method on alumina substrates on the wetting behavior, bond strength properties, and structure of interface in the Al/Al₂O₃ joints. Applying the sessile drop method, the wetting behavior of molten Al (99,999%) on coated alumina substrates was studied in the temperature range between 953 and 1373 K under a vacuum of 0.2 mPa for 30 min of contact. The sessile drop samples were used to examine the interface structure, shear strength, and interfacial fracture toughness under the concentrated load. The introduction of the thin Nb + Ti film layer of 900 nm thickness: (1) greatly improves the wettability of alumina by molten Al at above 1223 K and the shear strength of Al/Al₂O₃ joints produced at 1223 K, (2) has positive effect on structure transformation in the interface and leads to fabrication of reliable metal–ceramic joints. Microstructural investigations of the interface indicated that the precipitates of Nb and Ti-rich intermetallic phases were formed at the Al/Al₂O₃ interface, which influenced strengthening of these joints. Hence a conclusion can be drawn that the interface structure influences the durability increase in Al/Al₂O₃ joints.     

Dielectric behaviors of PHBHHx–BaTiO3 multifunctional composite films

Multifunctional polymeric composites were investigated for potential use in high energy storage capacitors and tissue engineering. The polymeric composites were fabricated by employing biodegradable polyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), as the matrix. Ferroelectric BaTiO₃ ceramic powders were added to the composites as fillers. The dielectric spectroscopy of the composites was measured over a wide frequency range (10⁰–10⁷ Hz) from −100 to 60 °C. The composition dependent dielectric behavior was modeled by a self-consistent effective medium theory. A percolation threshold of 0.367 was observed in the composites. The glass transition relaxation of the composite was also discussed by comparing the popular Vögel–Fulcher–Tammann law with a new glass model. The composites show attractive ferroelectricity and piezoelectricity for biomedical applications.     

含钛磷酸盐玻璃NaTi2(PO4)3-0.9Ca3(PO4)2的析晶行为

利用差热分析、X射线衍射仪、液氮吸附BET孔经测试仪对组成为NaTi2(PO4)3-0.9 Ca3(PO4)2的含钛磷酸盐玻璃的析晶行为进行了研究.通过对该玻璃相继进行成核、析晶和酸浸泡处理制备了NaTi2(PO4)3骨架多孔微晶玻璃.证明该玻璃在646℃8h成核处理过程中产生了旋节分解特征的成分偏聚,形成了富TiO2玻璃相和富CaO玻璃相交错生长的连通结构,成核处理后的玻璃在738℃析晶过程中依次在富钛相和富钙相中析出NaTi2(PO4)3和β-Ca3(PO4)2.成核过程对析晶的促进作用是通过促进NaTi2(PO4)3的析出而实现的.     

Si 含量对放电等离子烧结原位Nb/ Nb5Si3复合材料显微结构的影响

Nb/ Nb₅Si₃ 是一种新型的高温结构复合材料, 为了降低该材料的制备成本并有效控制材料的显微结构, 本文作者以Nb、Si 粉末为原料, 采用放电等离子烧结(SPS) 技术原位合成了近理论密度的Nb/ Nb₅Si₃ 复合材料, 着重研究了Si 含量对Nb/ Nb₅Si₃ 复合材料显微结构的影响。结果表明: 制备的复合材料由合成的Nb₅Si₃和均匀分布的Nb 颗粒组成; 在原子分数为6 %～20 %Si 范围内, 随着Si 含量增加, 复合材料中Nb₅Si₃ 数量增加, Nb 颗粒尺寸减小, 复合材料的致密性和硬度提高。      

Synthesis and photoluminescence properties of Eu-doped γ-Ca3(PO4)2

Eu³⁺-doped (1% and 3%) γ-Ca₃(PO₄)₂ was synthesized by high-pressure and high-temperature experimental method and the samples were characterized by X-ray diffraction. The luminescence properties of samples were investigated by emission and excitation spectra. The excitation spectra of Eu³⁺-doped γ-Ca₃(PO₄)₂ showed that samples were mainly attributed to Eu³⁺–O²⁻ charge-transfer band at 270 nm, and some sharp lines were also attributed to Eu³⁺ f–f transitions in near-UV regions with the strongest peaks at 395 nm. Under the 395 nm excitation, the intense red emission peak at 611 nm was observed. The strongest line (395 nm) in excitation spectra of those phosphors matched well with the output wavelength of UV InGaN-based light-emitting diodes (LEDs) chip. The luminescent properties suggested that Eu³⁺-doped γ-Ca₃(PO₄)₂ might be regarded as a potential red phosphor candidate for near-UV LEDs.